Young and old Professor X side-by-side...

Bryan Singer has tweeted the first behind-the-scenes picture from X-Men: Days of Future Past .

And while we knew Patrick Stewart was returning, this Professor X picture-related picture has us pretty excited about the time-travelling possibilities.

Singer's tweet ("Hello old friends #XMen #DaysofFuturePast") shows the young and old Professor X's wheelchairs side-by-side, teasing the inevitable cross-generational meet-up between James McAvoy and Patrick Stewart.

The story, which is widely renowned as one of the X-Men 's greatest comic adventures, introduces the idea of a bleak, dystopian future for Marvel's mutants, in which mutants are hunted to death or incarceration by giant mutant-killing robots known as Sentinels.